1. Technical Field
The present disclosure relates to a radio communication device that connects to a radio terminal as one of a plurality of access points to a communication network through radio communication using beam forming, and a communication control method.
2. Description of the Related Art
Millimeter wave communication, which requires no license and uses radio signals in the 60-GHz band while enabling high-speed communication, has been receiving attention in recent years.
Examples of major standards for wireless local area network (LAN) and wireless personal area network (PAN), which employ the millimeter wave communication, include Wireless Gigabit (WiGig), IEEE 802.15.3c, wireless high definition (WirelessHD), ECMA-387, and IEEE 802.11ad.
A millimeter wave band signal has radio-wave characteristics, which exhibit high linearity and large spatial attenuation. Thus, in many cases of the millimeter wave communication, which involves the above-described standards, beam forming techniques are used to control the directivity of the radio communication using a plurality of antennas.
Such beam forming techniques control the direction or width of a beam, which constitutes a communication area having directivity, and cause the beam to follow the position of a radio terminal, which is a communication partner. When a plurality of radio terminals are present in a range where a beam can be formed, which is hereinafter referred to as a “cell”, a millimeter wave communication device that uses the beam forming techniques connects to a plurality of radio terminals by switching the direction of the beam through time division.
The millimeter wave communication device can be used as a wireless access point to a communication network, such as the Internet. In this case, however, how to perform the handover of a radio terminal among a plurality of cells, that is, how to switch a connection destination matters.
Techniques for achieving high-speed roaming in non-directional communication are described in, for example, Japanese Unexamined Patent Application Publication No. 2011-4225. According to the techniques described in Japanese Unexamined Patent Application Publication No. 2011-4225, which are hereinafter referred to as the “conventional techniques”, an access point notifies information on another access point present on the periphery, such as a radio channel, a basic service set identification (BSSID), or an extended service set identification (ESSID), which is being used, to a radio terminal connecting to the access point. In reference to the notified information, the radio terminal narrows radio channels to be scanned at the time of roaming to another access point.
Such conventional techniques can reduce time needed for connection to another access point and enables handover to be performed at high speed.
When many radio terminals are present, an area with local concentration of radio terminals may be caused inside a whole communication area. In such a case, an access point near the area where the radio terminals are concentrated suffers heavy load and the communication quality of the radio terminal connecting to the access point decreases. Besides, when the radio terminals are concentrated in a direction inside a cell in the millimeter wave communication using the beam forming, multiplexing through frequency division or the like is necessary for a beam in the direction and the communication quality may further decrease.
Even when the connection destinations of the radio terminals are switched in such a situation, there may be more radio terminals at the switch destination access point. In addition, the beam at the switch destination access point may be used by more radio terminals. That is, the conventional techniques have an issue that, when local concentration of radio terminals occurs, particularly in the millimeter wave communication using a plurality of access points, the communication quality may decrease notably.